Where is it?

Berrygrove interchange, at M1 J5. It connects the main road north from London to an important dual carriageway route bypassing Watford and another important dual carriageway route into Watford.

It was spotted by Keith Mason.

What's wrong with it?

It's chronically, tragically, tear-jerkingly, desperately under capacity. Basically we have one roundabout to connect three dual carriageways heaving with traffic — or to put it another way, the interchanging movements between fourteen busy traffic lanes are carried out by three shared lanes. It's not pretty.

Why is it wrong?

It was never designed to be a particularly heavily-used junction at all. When it was built, the A4008 didn't exist, and so the very unusual double roundabout interchange design existed to let traffic hop between the M1 and A41, something that was possible further north and south of this junction. It did the job quite nicely. Then, some bright spark built a new dual carriageway from the centre of Watford to the M1. Not a bad idea.

The problem came when they saw a lovely roundabout with plenty of space to add a dual carriageway in. Add in the fact that Watford town centre is so busy that traffic regularly stacks back on the A4008 right out to this junction and you're starting to get the picture.

What would be better?

A very good question. The fact that the M1 and A41 are running parallel here is not good news in terms of junction design, and the fact that no remedy to the problem is even being considered by those in charge suggests ideas for this one are thin on the ground. I'm certainly having a hard time coming up with anything.

Right to reply

I use this junction all the time and at all times of the day, week and year. The worst I have ever known it is for the traffic to back up a bit down the various slip roads and down the A4008, the only exception being if there is an accident on any of the roads.

At rush hour, it beats Bushey Arches as a way into Watford from places like Edgware and Stanmore.

It's definitely a weird junction but generally works quite well for me.

Part of the problem at this junction is the poor road markings leading to dangerous change of lane. It is also the responsibility of Hertfordshire CC rather than the Highways Agency because of the access to the A41 and A4008.

If Herts could pull its finger out, a few cans of white paint could improve the traffic flow and safety on this junction considerably. There is also the problem of the lights coming onto the roundabout from the A4008 from Watfrod which are not very responsive to the traffic flows. Again Herts CC say there is nothing wrong.

The trouble with this junction is not that it is a dangerous all the time - it is dangerous only occasionally.

The greatest fault is that the carriageway has no lane markings save at the corners and no lane indicators (e.g. A41 or M1 South) other than at its Southwest corner. The danger caused is that traffic wishing to join the M1 South takes either the centre lane or the inside lane as they go round the roundabout. Unfortunately, traffic from the M1 North to any exit, also takes either the inside lane or the centre lane.

Therefore, if traffic from the M1 North to, say, the A4008 takes the inside lane, and traffic from the A4008 takes the centre lane to the M1 South, the former will be travelling across the M1 South junction as the latter is driving across it.

A colleague who is an accident investigator has a very fine template of this junction to copy into regular reports.

The A41/M1 junction at J5 of the M1 could easily be improved by NOT having the A41 link here and changing the layout at M1 J4, a few miles down the A41. This would leave just the A4008/M1 link at M1 J5 which would be easy.

Never have I seen the A4008 traffic backed up to the motorway. The main issue with it is the traffic lights. 1) They should be part time not full time as the amount of traffic at night is small enough to not need them, 2) If leaving the M1 southbound the green sequence is far too short which in rush hour tends to leave the slip road full, 3) There are too many sets of lights (one for each join) to go from A41 southbound to the A4008 you have to go through 5 sets of lights. A good example of limiting sets of lights is J19A of the M25 just 3 miles away for the M25,A41,A411 junction there is one set where the knock on effect of those lights make the junction flow very well.

What irritates me about this junction above all else is how much of the stress caused when using it is simply because of the totally illogical lane layouts.

For example, leaving the M1 Southbound and turning onto the A4008 towards Watford. There are three lanes on the approach to the roundabout:

Uninitiated drivers use the right hand lane, because to all intents and purposes, they believe they are turning right at the roundabout (in fact, its not the last exit because of its strange design).

The road markings advise the middle lane for the A4008 (no roadside signage of any kind here, that would be far to easy)

The locals use the left hand lane because they know that, contrary to every rule in the book, the first lane actually continues three quarters around the roundabout, past the M1 South, past the A41 south, and feeds directly into the A4008.

Cue chaos and catastrophe as everyone suddenly panics somewhere between the A41 and the A4008 exits and tries to change into a lane that might lead them where they want to go. (Urban legend has it that someone once took the innermost lane of the roundabout in 1997 and has been circling around trying to get out of it ever since...)

Try to apply the same logic in reverse though, and you will end up in another pickle as the A41 Northbound is in fact a lane drop from the roundabout (not sign-posted in advance, naturally!)

This is all while being held at several sets of lights that are grossly unfair and leave most the roundabout at a standstill while nobody moves in front of them.

Change the lanes to a 'whirlwind' type arrangement that guides drivers out to their respective routes, retime the lights and all is well with the world. That's how it appears to me anyway!

1: Start by extending the A4008 to Radlett. It'll give traffic somewhere to queue without blocking the junction, which leads on to
2: Widen the roundabout. Not to Simister levels, but add another lane around the outside. Don't forget flyovers for the new A4008 extension.
3: Add flyovers to the Colonial Road roundabout. Once again, this will prevent traffic snarling up into the Knutsford estate and the town centre.

So how about turning the M1/A41 here into a brief North American-style local/express system between where the M1 crosses under the A41 (or at J4 if money is more readily available) and J5 with more exits than the M1. It would remove the A41 from that weird roundabout structure (the remainder of the road would become a local road) and thus eliminate many conflicts. There might be *just* enough unbuilt land to fit such a system in. (And it wouldn't, quelle horreur!, encroach on any golf courses.)